The Event Horizon Telescope (EHT) collaboration has released Very Long Baseline Interferometry (VLBI) observations at the core of the M87* galaxy [1]}–[2]} and Milky Way galaxy [3]} with angular resolution comparable to that expected of a supermassive black hole. The EHT images show a dark central area called the black hole shadow which surrounded by a bright ring, the photon ring [4]}. These results consistent with predictions of the theory of general relativity (GR) [5]} and thus the EHT observations provide another strong evidence to Einstein’s theory. Synge was the first to investigate the deflection of light rays around a gravitationally intense star [6]}. Bardeen then argued that the shadow radius of static Schwarzschild black hole is \(r_{s}=3M\) , and also found that the angular momentum of rotating black holes deformed the shape of the shadow so that it’s not a perfect circle as the static case [7]}. Moreover, in recent years many studies about the black hole shadow in the context of different theories of gravity have been done [8]}–[9]}.
